Little background exists on producing monocrystal on insulator. Two approaches have been tried without much success. Both approaches, as does this invention, are performed on an insulator region formed on or in a single crystal substrate, usually silicon.
One approach is to mechanically place a crystalline seed on an insulator region, such as oxide, and then to thermally grow this crystalline seed. In this approach, there is the paramount problem of properly setting the seed so that the subsequent growth is of the correct alignment.
Another approach is to deposit a layer over the entire body and then to induce throughout the deposited layer monocrystalline growth using a pulsed laser. Although this approach does produce an epitaxial layer in the region of the deposited layer directly on the single crystal substrate, any extended growth over the insulator region will be either polycrystalline or amorphous in nature. This results from the impossibility of obtaining the appropriate uniform heat level throughout the deposited crystalline layer due to the differing thermal conductivity of the single crystal substrate and the insulator. This approach is discussed at length by Masao Tamura, Hiroshi Tamura and Takasi Tokuyama in "Si Building Epitaxy From Si Windows onto SiO.sub.2 by Q-Switched Ruby Laser Pulsed Annealing", Japanese Journal of Applied Physics, Vol. 19, No. 1, Jan., 1980, p. L23-26.
Clearly, neither approach produces the desired result of monocrystal on insulator combination. The monocrystal on insulator combination is an ideal basis for construction of semiconductor devices and circuits since it provides a region of insulation beneath the monocrystal to protect against device to device communication. Additionally, the insulator region allows denser packing of devices, higher speed capability, reduced susceptibility to latchup, and reduced susceptibility to ionizing radiation.